The invention relates to a process for the drying of natural substance extracts obtained by high-pressure extraction with liquefied gases or gases in the supercritical state.
It is known that a lower moisture content in extracts of natural substances results in an improvement in their stability in storage and in such practical properties as solubility and proportionability (German OS No. 2,627,534).
In the known extraction processes (solid-to-liquid or liquid-to-liquid) an attempt has been made to keep the moisture content low by using an extracting agent which does not mix with water, such as a hydrocarbon, for example. This method, however, is applicable only to natural substances in the pre-dried state. This method of extraction cannot be applied to plants or plant parts of high moisture content, since there is no assurance that the vegetable materials will be wetted by the organic extractant which is not miscible with water, and thus that all of the substances they contain will be extracted.
On the other hand, to reduce the moisture content of the extracted natural substances, extractants which are miscible with water are also used, such as alcohols for example. As a result, however, the solutions of the natural substance extracts thus prepared have to be heated to such an extent as to evaporate both the solvent and the water. This method, however, has considerable disadvantages on account of the great thermal stress on the natural substance extracts and the evaporation of a number of desirable components. Furthermore, an additional procedure is required in order to separate the solvent-and-water mixture.
In recent times a number of methods have become known in which the extraction of natural substances is performed with liquefied gases or with gases in the supercritical state (DE-OS No. 21 07 201, DE-PS No. 21 27 618, DE-PS No. 21 42 205, DE-AS No. 28 27 002, DE-AS No. 28 44 781 and DE-OS No. 29 05 078). The advantages of this extraction technique are the physiological acceptability of the extractant--carbon dioxide being used mostly for the purpose--as well as the extremely gentle treatment both of the extract and of the material being extracted, and the completeness of the extraction, since even the volatile components, especially the flavor substances, remain in the extract.
In this procedure the relatively high moisture content of the natural substance extracts has proven disadvantageous, especially in the extraction of fresh plants or plant parts. It has therefore been necessary heretofore to perform a complex after-treatment of the extracts if one is unwilling to forego one decided advantage of these methods, namely the low heat to which the extracts are subjected.
The object of the present invention consists in devising a method whereby it will be possible to dry in a simple and gentle manner the natural substance extracts obtained by high-pressure extraction with liquefied gases or gases in the supercritical state, without incurring losses of desired components, namely volatile components such as flavor substances.